1. Field of the Invention
The present invention relates to a method of making an image forming apparatus provided with an electron emission device.
2. Description of the Related Art
Conventional electron emission devices are classified into two types; they are thermion emission devices and cold-cathode electron emission devices. Further, the cold-cathode electron emission devices are classified into field emission types (hereinafter referred to as FE types), metal-insulating layer-metal types (hereinafter referred as MIM types), and surface conductive types.
FE types are disclosed by, for example, W. P. Dyke & W. W. Dolan, "Field Emission" (Advance in Electron Physics, 8, 89 (1956)) and C. A. Spindt, "Physical Properties of thin-film field emission cathodes with molybdenum cones" (J. Appl. Phys., 47, 5248 (1976)). MIM types are disclosed by, for example, C. A. Mead, "Operation of Tunnel-Emission Devices" (J. Appl. Phys., 32, 646 (1961)). Surface conductive type electron emission devices are disclosed by, for example, M. I. Elinson (Radio Eng. Electron Phys., 10, 1290 (1965)).
In the surface conductive type electron emission device, a current flowing parallel to a thin film, having a small area formed on a substrate, causes an electron emission phenomenon. The reported surface conductive type electron emission devices are composed of a SnO.sub.2 thin film as disclosed by Elinson, an Au thin film (G. Dittmer: "Thin Solid Films", 9, 317 (1972)), an In.sub.2 O.sub.3 /SnO.sub.2 thin film (M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)), and a carbon thin film (Hisashi Araki, et al., Shinku pk (Vacuum), 26(1), 22 (1983)).
In conventional surface conductive type electron emission devices, conductive thin films have generally been subjected to an energizing treatment (called "energizing forming") prior to electron emission to form an electron-emitting section. In the energizing forming treatment, a DC voltage or a significantly slowly increasing voltage of, for example, 1 V/min is applied between two ends of the conductive thin film to cause local destruction, deformation or modification of the conductive thin film, and thus to cause formation of an electron-emitting section having high electrical resistance. In the electron-emitting section, cracks form in a part of the conductive thin film, and electrons are emitted near the cracks. After the energizing forming treatment, a surface conductive type electron emission device emits electrons through the electron-emitting section when a voltage is applied to the conductive thin film to cause a current to flow in the device.
Since the surface conductive type electron emission device has a simplified configuration and can be readily formed, many devices can be arranged in a large area. Various applications, such as a charged beam source and a display device, have been studied to utilize such advantages. For example, in electron sources disclosed in Japanese Patent Laid-Open Nos. 64-31332, 1-283749, and 1-257552, surface conductive type electron emission devices are arranged in a matrix having many lines and rows, and devices in the same line are connected to each other at these ends with a lead line (called a common line). In image forming apparatuses such as display devices, planar display devices using liquid crystals have become widespread in place of cathode ray tubes (CRTs); however, those not having spontaneous luminescence inevitably require backlight sources. Accordingly, development of spontaneously luminescent display devices has been eagerly awaited. A typical example of the spontaneously luminescent display device has an electron source comprising an array of many surface conductive type electron emission devices and a fluorescent substance emitting visible light from electrons emerging from the electron source, as disclosed in U.S. Pat. No. 5,066,883.
In a conventional production process, an image forming apparatus using cold-cathode electron emission devices is produced by assembling a rear plate with an electron source composed of an array of cold-cathode electron emission devices, a face plate with a fluorescent substance for emitting visible light, a supporting frame provided outside the display region for maintaining a gap between the rear plate and the face plate, and an evacuation tube. In order to maintain atmospheric pressure, spacers may be used in the display region so as to maintain the gap between the face plate and the rear plate.
A frit compound may be used for adhering the rear and face plates to the supporting frame and spacers. Japanese Patent Laid-Open No. 8-138554 discloses the use of a frit compound to adhere the face and rear plates to the spacers, which are disposed in the display region of an image forming apparatus having a surface conductive type electron emission device in order to hold atmospheric pressure. This patent also discloses that when the frit compound is not applied to the rear plate having electron emission devices, electron emitting characteristics are affected less by the solvent and the binder in the frit compound during calcination of the frit compound.